<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="parent">
        <div class="test"></div>
    </div>
</body>
</html>

<style>
    /* 1.弹性盒 */
/* .parent{
    border:2px solid #333;
    width: 100px;
    height: 100px;
    display: flex;
    justify-content: center;
    align-items: center;
}
.test{
    width: 40px;
    height: 40px;
    background-color: pink;
    
} */

/* 2.定位 */
/* .parent{
    border:2px solid #333;
    width: 100px;
    height: 100px;
    position: relative;
}
.test{
    width: 40px;
    height: 40px;
    background-color: pink;
    position: absolute;
    top:27px;
    left: 30px;
} */


/* 3.怪异盒 */
.parent{
    border:2px solid #333;
    width: 100px;
    height: 100px;
    box-sizing: border-box;
}
.test{
    width: 40px;
    height: 40px;
    background-color: pink;
    margin-top:27px;
    margin-left: 30px;
}
</style>